added doc to dle encoder
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@ -1,95 +1,124 @@
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#include "DleEncoder.h"
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DleEncoder::DleEncoder() {
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}
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DleEncoder::~DleEncoder() {
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}
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ReturnValue_t DleEncoder::decode(const uint8_t *sourceStream,
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uint32_t sourceStreamLen, uint32_t *readLen, uint8_t *destStream,
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uint32_t maxDestStreamlen, uint32_t *decodedLen) {
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uint32_t encodedIndex = 0, decodedIndex = 0;
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uint8_t nextByte;
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if (*sourceStream != STX) {
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return RETURN_FAILED;
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}
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++encodedIndex;
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while ((encodedIndex < sourceStreamLen) && (decodedIndex < maxDestStreamlen)
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&& (sourceStream[encodedIndex] != ETX)
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&& (sourceStream[encodedIndex] != STX)) {
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if (sourceStream[encodedIndex] == DLE) {
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nextByte = sourceStream[encodedIndex + 1];
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if (nextByte == 0x10) {
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destStream[decodedIndex] = nextByte;
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} else {
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if ((nextByte == 0x42) || (nextByte == 0x43)
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|| (nextByte == 0x4D)) {
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destStream[decodedIndex] = nextByte - 0x40;
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} else {
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return RETURN_FAILED;
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}
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}
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++encodedIndex;
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} else {
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destStream[decodedIndex] = sourceStream[encodedIndex];
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}
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++encodedIndex;
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++decodedIndex;
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}
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if (sourceStream[encodedIndex] != ETX) {
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return RETURN_FAILED;
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} else {
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*readLen = ++encodedIndex;
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*decodedLen = decodedIndex;
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return RETURN_OK;
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}
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}
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ReturnValue_t DleEncoder::encode(const uint8_t* sourceStream,
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uint32_t sourceLen, uint8_t* destStream, uint32_t maxDestLen,
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uint32_t* encodedLen, bool addStxEtx) {
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if (maxDestLen < 2) {
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return RETURN_FAILED;
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}
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uint32_t encodedIndex = 0, sourceIndex = 0;
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uint8_t nextByte;
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if (addStxEtx) {
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destStream[0] = STX;
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++encodedIndex;
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}
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while ((encodedIndex < maxDestLen) && (sourceIndex < sourceLen)) {
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nextByte = sourceStream[sourceIndex];
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if ((nextByte == STX) || (nextByte == ETX) || (nextByte == 0x0D)) {
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if (encodedIndex + 1 >= maxDestLen) {
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return RETURN_FAILED;
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} else {
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destStream[encodedIndex] = DLE;
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++encodedIndex;
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destStream[encodedIndex] = nextByte + 0x40;
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}
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} else if (nextByte == DLE) {
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if (encodedIndex + 1 >= maxDestLen) {
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return RETURN_FAILED;
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} else {
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destStream[encodedIndex] = DLE;
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++encodedIndex;
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destStream[encodedIndex] = DLE;
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}
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} else {
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destStream[encodedIndex] = nextByte;
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}
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++encodedIndex;
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++sourceIndex;
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}
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if ((sourceIndex == sourceLen) && (encodedIndex < maxDestLen)) {
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if (addStxEtx) {
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destStream[encodedIndex] = ETX;
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++encodedIndex;
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}
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*encodedLen = encodedIndex;
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return RETURN_OK;
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} else {
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return RETURN_FAILED;
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}
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}
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#include "../globalfunctions/DleEncoder.h"
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DleEncoder::DleEncoder() {}
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DleEncoder::~DleEncoder() {}
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ReturnValue_t DleEncoder::encode(const uint8_t* sourceStream,
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size_t sourceLen, uint8_t* destStream, size_t maxDestLen,
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size_t* encodedLen, bool addStxEtx) {
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if (maxDestLen < 2) {
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return STREAM_TOO_SHORT;
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}
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size_t encodedIndex = 0, sourceIndex = 0;
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uint8_t nextByte;
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if (addStxEtx) {
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destStream[0] = STX_CHAR;
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++encodedIndex;
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}
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while (encodedIndex < maxDestLen and sourceIndex < sourceLen)
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{
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nextByte = sourceStream[sourceIndex];
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// STX, ETX and CR characters in the stream need to be escaped with DLE
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if (nextByte == STX_CHAR or nextByte == ETX_CHAR or nextByte == CARRIAGE_RETURN) {
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if (encodedIndex + 1 >= maxDestLen) {
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return STREAM_TOO_SHORT;
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}
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else {
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destStream[encodedIndex] = DLE_CHAR;
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++encodedIndex;
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/* Escaped byte will be actual byte + 0x40. This prevents
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* STX, ETX, and carriage return characters from appearing
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* in the encoded data stream at all, so when polling an
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* encoded stream, the transmission can be stopped at ETX.
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* 0x40 was chosen at random with special requirements:
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* - Prevent going from one control char to another
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* - Prevent overflow for common characters */
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destStream[encodedIndex] = nextByte + 0x40;
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}
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}
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// DLE characters are simply escaped with DLE.
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else if (nextByte == DLE_CHAR) {
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if (encodedIndex + 1 >= maxDestLen) {
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return STREAM_TOO_SHORT;
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}
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else {
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destStream[encodedIndex] = DLE_CHAR;
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++encodedIndex;
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destStream[encodedIndex] = DLE_CHAR;
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}
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}
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else {
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destStream[encodedIndex] = nextByte;
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}
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++encodedIndex;
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++sourceIndex;
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}
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if (sourceIndex == sourceLen and encodedIndex < maxDestLen) {
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if (addStxEtx) {
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destStream[encodedIndex] = ETX_CHAR;
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++encodedIndex;
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}
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*encodedLen = encodedIndex;
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return RETURN_OK;
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}
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else {
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return STREAM_TOO_SHORT;
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}
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}
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ReturnValue_t DleEncoder::decode(const uint8_t *sourceStream,
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size_t sourceStreamLen, size_t *readLen, uint8_t *destStream,
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size_t maxDestStreamlen, size_t *decodedLen) {
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size_t encodedIndex = 0, decodedIndex = 0;
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uint8_t nextByte;
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if (*sourceStream != STX_CHAR) {
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return DECODING_ERROR;
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}
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++encodedIndex;
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while ((encodedIndex < sourceStreamLen) && (decodedIndex < maxDestStreamlen)
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&& (sourceStream[encodedIndex] != ETX_CHAR)
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&& (sourceStream[encodedIndex] != STX_CHAR)) {
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if (sourceStream[encodedIndex] == DLE_CHAR) {
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nextByte = sourceStream[encodedIndex + 1];
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// The next byte is a DLE character that was escaped by another
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// DLE character, so we can write it to the destination stream.
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if (nextByte == DLE_CHAR) {
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destStream[decodedIndex] = nextByte;
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}
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else {
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/* The next byte is a STX, DTX or 0x0D character which
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* was escaped by a DLE character. The actual byte was
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* also encoded by adding + 0x40 to preven having control chars,
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* in the stream at all, so we convert it back. */
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if (nextByte == 0x42 or nextByte == 0x43 or nextByte == 0x4D) {
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destStream[decodedIndex] = nextByte - 0x40;
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}
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else {
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return DECODING_ERROR;
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}
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}
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++encodedIndex;
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}
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else {
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destStream[decodedIndex] = sourceStream[encodedIndex];
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}
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++encodedIndex;
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++decodedIndex;
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}
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if (sourceStream[encodedIndex] != ETX_CHAR) {
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*readLen = ++encodedIndex;
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return DECODING_ERROR;
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}
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else {
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*readLen = ++encodedIndex;
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*decodedLen = decodedIndex;
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return RETURN_OK;
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}
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}
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@ -1,25 +1,79 @@
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#ifndef DLEENCODER_H_
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#define DLEENCODER_H_
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#include "../returnvalues/HasReturnvaluesIF.h"
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class DleEncoder: public HasReturnvaluesIF {
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private:
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DleEncoder();
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virtual ~DleEncoder();
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public:
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static const uint8_t STX = 0x02;
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static const uint8_t ETX = 0x03;
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static const uint8_t DLE = 0x10;
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static ReturnValue_t decode(const uint8_t *sourceStream,
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uint32_t sourceStreamLen, uint32_t *readLen, uint8_t *destStream,
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uint32_t maxDestStreamlen, uint32_t *decodedLen);
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static ReturnValue_t encode(const uint8_t *sourceStream, uint32_t sourceLen,
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uint8_t *destStream, uint32_t maxDestLen, uint32_t *encodedLen,
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bool addStxEtx = true);
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};
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#endif /* DLEENCODER_H_ */
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#ifndef FRAMEWORK_GLOBALFUNCTIONS_DLEENCODER_H_
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#define FRAMEWORK_GLOBALFUNCTIONS_DLEENCODER_H_
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#include "../returnvalues/HasReturnvaluesIF.h"
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#include <cstddef>
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/**
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* @brief This DLE Encoder (Data Link Encoder) can be used to encode and
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* decode arbitrary data with ASCII control characters
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* @details
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* List of control codes:
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* https://en.wikipedia.org/wiki/C0_and_C1_control_codes
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*
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* This encoder can be used to achieve a basic transport layer when using
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* char based transmission systems.
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* The passed source strean is converted into a encoded stream by adding
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* a STX marker at the start of the stream and an ETX marker at the end of
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* the stream. Any STX, ETX, DLE and CR occurences in the source stream are
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* escaped by a DLE character. The encoder also replaces escaped control chars
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* by another char, so STX, ETX and CR should not appear anywhere in the actual
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* encoded data stream.
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*
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* When using a strictly char based reception of packets enoded with DLE,
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* STX can be used to notify a reader that actual data will start to arrive
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* while ETX can be used to notify the reader that the data has ended.
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*/
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class DleEncoder: public HasReturnvaluesIF {
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private:
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DleEncoder();
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virtual ~DleEncoder();
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public:
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static constexpr uint8_t INTERFACE_ID = CLASS_ID::DLE_ENCODER;
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static constexpr ReturnValue_t STREAM_TOO_SHORT = MAKE_RETURN_CODE(0x01);
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static constexpr ReturnValue_t DECODING_ERROR = MAKE_RETURN_CODE(0x02);
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//! Start Of Text character. First character is encoded stream
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static constexpr uint8_t STX_CHAR = 0x02;
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//! End Of Text character. Last character in encoded stream
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static constexpr uint8_t ETX_CHAR = 0x03;
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//! Data Link Escape character. Used to escape STX, ETX and DLE occurences
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//! in the source stream.
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static constexpr uint8_t DLE_CHAR = 0x10;
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static constexpr uint8_t CARRIAGE_RETURN = 0x0D;
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/**
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* Encodes the give data stream by preceding it with the STX marker
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* and ending it with an ETX marker. STX, ETX and DLE characters inside
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* the stream are escaped by DLE characters and also replaced by adding
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* 0x40 (which is reverted in the decoing process).
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* @param sourceStream
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* @param sourceLen
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* @param destStream
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* @param maxDestLen
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* @param encodedLen
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* @param addStxEtx
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* Adding STX and ETX can be omitted, if they are added manually.
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* @return
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*/
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static ReturnValue_t encode(const uint8_t *sourceStream, size_t sourceLen,
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uint8_t *destStream, size_t maxDestLen, size_t *encodedLen,
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bool addStxEtx = true);
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/**
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* Converts an encoded stream back.
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* @param sourceStream
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* @param sourceStreamLen
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* @param readLen
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* @param destStream
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* @param maxDestStreamlen
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* @param decodedLen
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* @return
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*/
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static ReturnValue_t decode(const uint8_t *sourceStream,
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size_t sourceStreamLen, size_t *readLen, uint8_t *destStream,
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size_t maxDestStreamlen, size_t *decodedLen);
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};
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#endif /* FRAMEWORK_GLOBALFUNCTIONS_DLEENCODER_H_ */
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